Traumatic brain injuries represent an important health problem: they occur with high frequency, the population affected contains many previously healthy young people, and they are associated with high mortality and morbidity. This proposal is to become one of up to 8 sites in a Traumatic Brain Injury Clinical Trials Network that will collect longitudinal data on people with traumatic brain injury and conduct (with separate funding) multi-center clinical trials of interventions to improve the treatment and outcome of people who sustain a traumatic brain injury. The aims of the application are to achieve the goals of the Traumatic Brain Injury Network by collaborating with other Network sites and with NICHD staff to recruit patients into Network studies, by evaluating and treating patients according to Network protocols, by proposing and suggesting modifications to clinical intervention protocols, and by proposing and suggesting modifications to outcome measures. The proposal summarizes the abilities of the University of Washington to contribute to the Network and proposes a concept protocol that the Network might consider for one of the multicenter trials. Using a randomized. double-blind design, the concept protocol evaluates magnesium sulfate as a neuroprotectant and anti-epileptogenic agent following head injury. Magnesium sulfate is a widely used, well-tolerated compound that has been shown in the laboratory to be effective in reducing seizures and also in limiting neuronal damage and in improving functional outcome following experimental head injury. Specifically, the study will test the hypothesis that magnesium sulfate, when given within 8 hours of a moderate or severe head injury, (a) increases survival, (b) decreases seizures, and (c) improves neurobehavioral functioning. Additionally, the study will assess the effects of timing of dosage (e.g. <4 hours vs. 4-8 hours), gender, and race, and determine the rate of adverse events.